A continuous forming method of an ultrahigh molecular weight polyethylene rod

Abstract

The application relates to the technical field of high polymer product processing, and particularly discloses a continuous forming method of an ultrahigh molecular weight polyethylene rod material. The continuous forming method of the ultrahigh molecular weight polyethylene rod material adds pure UHMWPE powder with a molecular weight of 2 million-6.5 million into a single-screw extruder, sets processing parameters, and adopts a working mode of a circumferential uniform-speed rotation superimposed on a reciprocating swing variable-speed rotation mode of the screw in the single-screw extruder to extrude and extrude the UHMWPE powder; the UHMWPE powder is subjected to high-temperature plasticization, continuous extrusion, rod cooling, and finally cutting forming, and the medical-grade UHMWPE powder with a molecular weight of 6.5 million can be continuously processed into ultraclean rod material with a smooth surface, dense material and a maximum diameter of 80 mm without adding an additive in the preparation process, so that the generation efficiency and the mechanical properties of the UHMWPE rod material can be effectively improved; the method can be used for preparing high-wear-resistance liners, ultraclean medical-grade artificial joints or impact-wear-resistance parts such as bearings and gears of large machines.

Description

Technical Field

[0001] This invention relates to the field of polymer processing technology, specifically to a continuous molding method for ultra-high molecular weight polyethylene rods. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is a common name for a class of linear polymers containing ethylene units, wherein the polymer has a molecular weight of approximately 1-1.5 × 10⁻⁶. 6 Ultra-high molecular weight polyethylene (UHMWPE) has a weight-average molecular weight of g / mol or even higher. It possesses many excellent properties, including good abrasion resistance, high impact strength, low-temperature resistance, chemical resistance, good insulation, and non-toxicity. Therefore, it has wide applications in textiles, military, packaging, transportation, petroleum, food, machinery, construction, electrical, medical, and sports industries, such as artificial joints, blood transfusion pumps, cables, pipes, battery separators, subway track pads, gear rollers, helmets, bulletproof vests, and bulletproof vests.

[0003] However, due to severe chain entanglement caused by the long, flexible linear molecular chains, UHMWPE exhibits high viscosity above its melting point, with a zero-shear melt viscosity reaching 10. 8 At speeds above Pa·s, the melt flow index approaches 0, and the critical shear rate is low. Melt fracture occurs even at very slow shear speeds, easily leading to rough surfaces and structural defects in molded products. Therefore, the molding and processing of UHMWPE is very difficult. Consequently, the preparation of thick-walled UHMWPE molding compounds often requires the addition of large amounts of plasticizers or blending with other low-molecular-weight polymers to improve its processability. To improve the extrusion processability of pure UHMWPE powder, patents CN1478811, CN1488668, and CN103751849A employ blending strategies to modify the material system. While introducing relatively low-molecular-weight polymers (such as polypropylene and high-density polyethylene) can improve melt flowability, it also significantly degrades the physical and mechanical properties of UHMWPE itself. Furthermore, due to the stringent requirements for biosafety and cleanliness of some special-purpose UHMWPE materials, such as medical implants, no processing aids, including plasticizers, lubricants, and release agents, are allowed to be added during the molding process to avoid introducing other impurities or components. Only pure UHMWPE powder can be used for molding and processing. Therefore, researching the processing methods of thick pure UHMWPE products has great practical value.

[0004] Currently, the main molding methods for pure UHMWPE molding compounds include compression molding and sintering, hot isostatic pressing (HIP), and plunger extrusion. Patents WO03 / 031140A1 and CN1654192 use compression molding and sintering and HIP, respectively, to prepare pure UHMWPE profiles; compression molding and sintering is the traditional and earliest applied UHMWPE molding method, while HIP is a relatively new method. However, both are intermittent molding technologies, resulting in low production efficiency and difficulty in ensuring product quality stability. Plunger extrusion enables continuous molding, using a reciprocating piston motion to move the material forward, and can be used to prepare molding compound rods. Since no shear force field is applied to the material, plunger extrusion can essentially be considered a continuous compression molding and sintering process. However, the production efficiency of plunger extrusion remains low, and the mechanical properties of the rods are not ideal. Some researchers have improved plunger extrusion, attempting to achieve continuous extrusion processing of pure UHMWPE through screw shearing action. Patent CN101474860 controls the barrel temperature within a low range, allowing pure UHMWPE with a molecular weight of over 3 million to be solid-state conveyed within a single-screw extruder and then formed in a die. South China University of Technology has developed an eccentric rotor extrusion device to extrude UHMWPE with a molecular weight of 2.5 million, and then uses the pre-treated molten plasticized UHMWPE for compression molding to obtain the finished product. These screw extrusion technologies have not achieved continuous molding of UHMWPE rods. In summary, efficient, continuous, and stable molding of pure UHMWPE rods remains quite difficult and challenging. Furthermore, large-diameter medical-grade rods are suitable for manufacturing artificial joint prostheses (such as knee joint friction pads) and possess extremely high added value. Therefore, developing new methods for continuous molding of pure UHMWPE rods has significant practical implications. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a continuous molding method and preparation apparatus for ultra-high molecular weight polyethylene (UHMWPE) rods that effectively improves the production efficiency and physical and mechanical properties of large-diameter rods. This apparatus enables the continuous molding of ultra-clean, large-diameter UHMWPE rods from UHMWPE powder with a molecular weight up to 650W without the addition of additives. Because the resulting rods have a high molecular weight and are pure, they can be used to prepare ultra-clean medical-grade artificial joints, high-wear-resistant pads, or impact-resistant and wear-resistant parts for large machinery, such as bearings and gears.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows:

[0007] The first technical problem to be solved by this invention is to provide a method for the continuous molding of ultra-high molecular weight polyethylene rods, comprising the following steps:

[0008] S1. Select medical-grade UHMWPE powder;

[0009] S2. Add the selected UHMWPE powder to a single-screw extruder, set the processing parameters, and after high-temperature plasticizing, continuous extrusion, rod cooling, and finally cutting into shape;

[0010] The single-screw extruder uses a variable angular velocity rotation mode, which combines circumferential uniform rotation with reciprocating oscillation, to extrude and extrude UHMWPE powder.

[0011] Furthermore, the molecular weight of the UHMWPE powder in step S1 is 2 million to 6.5 million.

[0012] Furthermore, the continuous molding preparation method for ultra-high molecular weight polyethylene rods described in this invention achieves the preparation of UHMWPE rods using a continuous molding preparation device for ultra-high molecular weight polyethylene rods.

[0013] The equipment for the continuous molding of ultra-high molecular weight polyethylene rods includes a single screw extruder, a power control box, an extrusion die, a cooling and shaping device, a traction guide rail, and a pneumatic cutting machine.

[0014] The single-screw extruder has a barrel and a screw; the inner wall of the barrel is provided with a threaded structure and the thread direction of the threaded structure is opposite to the thread direction of the screw;

[0015] The single-screw extruder uses a servo motor to drive its screw, and a reducer is installed inside the single-screw extruder, which is connected to the servo motor for transmission.

[0016] The single-screw extruder also includes a controller. The servo motor and reducer are respectively connected to the controller via signals. The controller is used to control the screw to perform circumferential uniform rotation superimposed with reciprocating oscillation and variable angular velocity rotation.

[0017] Furthermore, the processing parameters set in step S2 include control parameters for the screw's circumferential uniform rotation superimposed with reciprocating oscillation and variable angular velocity rotation; specifically, the screw's uniform rotation speed, oscillation frequency, and oscillation amplitude.

[0018] The screw rotates at a constant angular velocity of The angular velocity of the screw's reciprocating oscillation is ;

[0019]

[0020] In the formula, f is the oscillation frequency. This refers to the amplitude of the oscillation.

[0021] The sum of the angular velocity of the screw rotating at a constant speed and the angular velocity of the screw reciprocating oscillation yields the positive superimposed velocity V1 and the negative superimposed velocity V2.

[0022]

[0023]

[0024] Where, when V2 > 0, the direction of rotation of V2 is... The rotation direction is the same as that of V2; when V2 < 0, the rotation direction of V2 is the same as that of V2. The rotation direction is opposite.

[0025] Preferably, the uniform rotation speed is 0.5 to 5 rpm, the oscillation frequency is 0.1 to 2 Hz, and the oscillation amplitude is 1.57 to 6.28 rad.

[0026] Furthermore, a temperature measuring coupler and a pressure sensor are provided on the extrusion die.

[0027] Furthermore, the temperature of the barrel is divided into 7 sections from the feed inlet to the extrusion die. The temperature of the first to the fourth section gradually increases, and the temperature of the fourth to the seventh section gradually decreases. The temperature adjustment range of the barrel is between 90°C and 260°C.

[0028] Furthermore, in step S2, the temperature of the barrel is controlled to be 90℃, 180℃, 220℃, 260℃, 250℃, 240℃, and 180℃ respectively from the first to the seventh stage.

[0029] Furthermore, the pressure of the extrusion die is less than or equal to 60 MPa, furthermore, the pressure of the extrusion die is less than 20 MPa, and even further, the pressure of the extrusion die is less than 10 MPa.

[0030] Furthermore, the screw has a diameter of Φ70mm and a length-to-diameter ratio of 26:1.

[0031] The second technical problem to be solved by the present invention is to provide an ultra-high molecular weight polyethylene rod, which is prepared by the above method.

[0032] The third technical problem to be solved by the present invention is to apply the above-mentioned ultra-high molecular weight polyethylene rods to the manufacture of medical-grade artificial joints, high wear-resistant pads, or impact-resistant and wear-resistant parts of large machinery such as bearings and gears.

[0033] The fourth technical problem to be solved by this invention is to provide a method for improving the mechanical properties (impact strength or breaking strength, etc.) of ultra-high molecular weight polyethylene rods, the method comprising the following steps:

[0034] S1. Select medical-grade UHMWPE powder;

[0035] S2. Add the selected UHMWPE powder to a single-screw extruder, set the processing parameters, and after high-temperature plasticizing, continuous extrusion, rod cooling, and finally cutting into shape;

[0036] The single-screw extruder uses a variable angular velocity rotation mode, which combines circumferential uniform rotation with reciprocating oscillation, to extrude and extrude UHMWPE powder.

[0037] Furthermore, the molecular weight of the UHMWPE powder in step S1 is 2 million to 6.5 million.

[0038] Furthermore, the method employs the following preparation apparatus, which includes a single-screw extruder, a power control box, an extrusion die, a cooling and shaping device, a traction guide rail, and a pneumatic cutter, as described in step S2. The single-screw extruder has a threaded structure on the inner wall of its barrel, and the thread direction of the threaded structure is opposite to that of the screw.

[0039] The single-screw extruder uses a servo motor to drive its screw, and a reducer is installed inside the single-screw extruder, which is connected to the servo motor drive.

[0040] The single-screw extruder is equipped with a programmable controller. The servo motor and reducer are respectively connected to the programmable controller via signals. The programmable controller is used to control the screw to perform circumferential uniform rotation superimposed with reciprocating oscillation at a variable angular velocity.

[0041] Furthermore, the control parameters for the screw's circumferential uniform rotation superimposed with reciprocating oscillation with variable angular velocity rotation are specifically the screw's uniform rotation speed, oscillation frequency, and oscillation amplitude.

[0042] The screw rotates at a constant angular velocity of The angular velocity of the screw's reciprocating oscillation is ;

[0043]

[0044] In the formula, f is the oscillation frequency. This refers to the amplitude of the oscillation.

[0045] The sum of the angular velocity of the screw rotating at a constant speed and the angular velocity of the screw reciprocating oscillation yields the positive superimposed velocity V1 and the negative superimposed velocity V2.

[0046]

[0047]

[0048] Where, when V2 > 0, the direction of rotation of V2 is... The rotation direction is the same as that of V2; when V2 < 0, the rotation direction of V2 is the same as that of V2. The rotation direction is opposite.

[0049] Preferably, the uniform rotation speed is 0.5 to 5 rpm, the oscillation frequency is 0.1 to 2 Hz, and the oscillation amplitude is 1.57 to 6.28 rad.

[0050] Furthermore, a temperature measuring coupler and a pressure sensor are provided on the extrusion die.

[0051] Furthermore, the temperature of the barrel is divided into 7 sections from the feed inlet to the extrusion die. The temperature of the first to the fourth section gradually increases, and the temperature of the fourth to the seventh section gradually decreases. The temperature adjustment range of the barrel is between 90°C and 260°C.

[0052] Furthermore, the temperatures of the barrel from the first to the seventh section are 90℃, 180℃, 220℃, 260℃, 250℃, 240℃, and 180℃, respectively.

[0053] Furthermore, the pressure of the extrusion die is less than or equal to 60 MPa, furthermore, the pressure of the extrusion die is less than 20 MPa, and even further, the pressure of the extrusion die is less than 10 MPa.

[0054] Furthermore, the screw has a diameter of Φ70mm and a length-to-diameter ratio of 26:1.

[0055] The beneficial effects of this invention are:

[0056] 1. Without adding any processing aids, the preparation method provided by this invention can continuously process medical-grade UHMWPE powder with a molecular weight of 6.5 million into ultra-clean rods with smooth surfaces, dense materials, and a maximum diameter of Φ80mm, which can be used to prepare ultra-clean medical-grade artificial joints. Compared with conventional molding methods (uniform screw rotation), the variable angular velocity rotary extrusion technology with circumferential uniform rotation and reciprocating oscillation (variable angular velocity screw rotation) can significantly improve the production efficiency and mechanical properties of the rods.

[0057] 2. In the preparation method provided by the present invention, the screw of the extruder operates in a variable angular velocity rotation state, and the rotation speed changes periodically with regular acceleration and deceleration. By utilizing the improved screw working mode, the production efficiency and physical and mechanical properties of large-diameter bars are effectively improved, which is suitable for the production of high wear-resistant pads or impact-resistant wear-resistant parts of large machinery such as bearings and gears.

[0058] 3. In this invention, the threads on the inner wall of the barrel and the screw are opposite in direction, and their tight fit enhances the local extrusion effect, which is beneficial for material fusion and homogenization. Furthermore, when the material is in a solid or semi-solid state, it corresponds to screw extrusion mode, while when the material is in a molten state, it corresponds to plunger extrusion mode. Combining the characteristics of screw extrusion and plunger extrusion achieves continuous and stable molding of UHMWPE rods and effectively mitigates molecular weight degradation. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the preparation device for continuous molding of ultra-high molecular weight polyethylene rods in an embodiment of the present invention;

[0060] Figure 2 This is a schematic diagram of the barrel structure of the single-screw extruder in an embodiment of the present invention;

[0061] Figure 3 This is a schematic diagram of the screw structure of the single-screw extruder in an embodiment of the present invention;

[0062] Figure 4 This is a schematic diagram of the UHMWPE rod in an embodiment of the present invention; the diameter of the UHMWPE rod in the figure is Φ;

[0063] Figure 5 The image shows a physical picture of UHMWPE rods produced by the method and equipment of the present invention in an embodiment of the present invention; in the picture, the UHMWPE rods have a smooth surface, dense and defect-free material, and a diameter Φ of 80mm.

[0064] Figure 6 The tensile stress-strain curves are for Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3.

[0065] Figure 7 This is a schematic diagram illustrating the principle of uniform screw rotation in an embodiment of the present invention;

[0066] Figure 8 This is a graph showing the relationship between the angular velocity of the screw reciprocating and oscillating and time in an embodiment of the present invention;

[0067] Figure 8 middle Figure 8 a is a graph showing the relationship between the oscillation velocity and time when the initial rotational direction of the oscillation angular velocity is the same as the rotational direction of the screw at a constant speed. Figure 8 b is a graph showing the relationship between the oscillation velocity and time when the initial rotation direction of the oscillation angular velocity is opposite to the rotation direction of the screw at a constant speed;

[0068] Figure 9 In this embodiment of the invention, the reciprocating oscillation is... Figure 8In case a, when the screw's uniform rotational angular velocity and the screw's reciprocating oscillation angular velocity are superimposed, and V2 > 0, the screw rotation diagram is shown.

[0069] Figure 10 In this embodiment of the invention, the reciprocating oscillation is... Figure 8 In case a, after the sum of the angular velocity of the screw's uniform rotation and the angular velocity of the screw's reciprocating oscillation, when V2=0, the schematic diagram of the screw's rotation is shown.

[0070] Figure 11 In this embodiment of the invention, the reciprocating oscillation is... Figure 8 In case a, when the screw's uniform rotational angular velocity and the screw's reciprocating oscillation angular velocity are superimposed, and V2 < 0, the screw rotation diagram is shown.

[0071] Figure 12 In this embodiment of the invention, the reciprocating oscillation is... Figure 8 In case b, when the screw's uniform rotational angular velocity and the screw's reciprocating oscillation angular velocity are superimposed, and V2 > 0, the screw rotation diagram is shown.

[0072] The diagram shows: 1-Power distribution control box, 2-Single screw extruder, 21-Barrel, 22-Threaded structure, 23-Screw, 3-Extrusion die, 4-Cooling and shaping device, 41-Coolant inlet pipe, 5-Traction guide rail, 6-Pneumatic cutting machine, 7-UHMWPE bar, 71-UHMWPE bar cross-section. Detailed Implementation

[0073] The specific embodiments of this utility model will be further described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0074] It should be noted that all directional indicator terms such as "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" in the embodiments of this application indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. They are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0075] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0076] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0077] A method for continuously molding ultra-high molecular weight polyethylene rods includes the following steps:

[0078] S1. Select pure UHMWPE powder;

[0079] S2. Add the selected UHMWPE powder to a single-screw extruder, set the processing parameters, and after high-temperature plasticizing, continuous extrusion, rod cooling, and finally cutting into shape;

[0080] The screw 23 of the single-screw extruder uses a variable angular velocity rotation mode of circumferential uniform rotation superimposed with reciprocating oscillation to extrude and extrude UHMWPE powder.

[0081] In this embodiment, preferably, the molecular weight of the UHMWPE powder in step S1 is 2 million to 6.5 million.

[0082] In this embodiment, a continuous molding apparatus for ultra-high molecular weight polyethylene (UHMWPE) rods is used to prepare UHMWPE rods; specifically, as shown... Figure 1 , 2 as well as Figure 3As shown, a continuous molding preparation device for ultra-high molecular weight polyethylene rods includes a single screw extruder 2, an electrical control box 1, an extrusion die 3, a cooling and shaping device 4, a traction guide rail 5, and a pneumatic cutting machine 6. The electrical control box, extrusion die, cooling and shaping device, traction guide rail, and pneumatic cutting machine are all existing technologies known to those skilled in the art and will not be described in detail here.

[0083] The single-screw extruder 2 includes an extruder body, the structure of which adopts the existing structure of a conventional single-screw extruder. In this embodiment, the barrel 21 and screw 23 of the single-screw extruder 2 are configured to achieve continuous production of UHMWPE rods, thereby improving production efficiency and the mechanical properties of UHMWPE rods.

[0084] Specifically, the inner wall of the barrel 21 of the single screw extruder 2 is provided with a threaded structure 22, and the thread direction of the threaded structure 22 is opposite to that of the screw 23. The reversed thread setting can effectively prevent material blockage. The thread directions of the barrel 21 and the screw 23 are matched to each other, which strengthens the local extrusion effect.

[0085] The single-screw extruder 2 uses a servo motor to drive its screw 23. The single-screw extruder is equipped with a reducer, which is connected to the servo motor. Specifically, the servo motor provides power, and the reducer is used to adjust the speed.

[0086] The working principle of screw 23 achieving circumferential uniform rotation superimposed with reciprocating oscillation is as follows: A servo motor drives a reducer to rotate, which in turn drives screw 23. During the uniform rotation of screw 23, it intermittently rotates a distance in the opposite direction, pauses intermittently, decreases its rotational speed for a distance, or accelerates its rotation in the direction of rotation for a distance; this reciprocating oscillation occurs repeatedly. This superposition of the screw's reciprocating oscillation trajectory during the uniform rotation of screw 23 is achieved. The frequency of the oscillation and the amplitude of the rotational distance can both be adjusted by controlling the servo motor. Specifically, the frequency and amplitude are set according to the process requirements.

[0087] Specifically, the screw 23 rotates at a constant angular velocity of... The angular velocity of the reciprocating oscillation of screw 23 is ;

[0088]

[0089] In the formula, f is the oscillation frequency. This refers to the amplitude of the oscillation.

[0090] The angular velocity of the screw 23 rotating at a constant speed and the angular velocity of the screw 23 reciprocating oscillation are superimposed to obtain the positive superimposed velocity V1 and the negative superimposed velocity V2;

[0091]

[0092]

[0093] Where, when V2 > 0, the direction of rotation of V2 is... The rotation direction is the same as that of V2; when V2 < 0, the rotation direction of V2 is the same as that of V2. The rotation direction is opposite.

[0094] In the application process, such as Figure 7 The diagram shows a screw rotating at a constant speed and a graph of the rotation speed versus time; the screw 23 rotates at a speed of... Rotating at a constant speed;

[0095] like Figure 8 The figure shows the curve of oscillation speed versus time, where the screw 23 rotates in the positive direction at a constant speed when the oscillation speed is positive, and the screw 23 rotates in the opposite direction when the oscillation speed is negative.

[0096] like Figure 9 The diagram shows the rotation when the initial rotational direction of the oscillating angular velocity of screw 23 is the same as the direction of its uniform rotation, and the sum of the uniform rotational angular velocity and the angular velocity of the reciprocating oscillation of screw 23, with V2 > 0; V2 > 0 indicates that the rotational direction of V2 is the same as the direction of the screw's uniform rotation. The rotation direction is the same; that is, during the uniform rotation of screw 23, when oscillation occurs, the screw 23 will experience a process where its rotational speed increases to V1 for a period of time, then decreases to V2 for a period of time, and then repeats this process of increasing to V1 for a period of time and decreasing to V2 for a period of time, until the oscillation ends, and screw 23 continues to rotate in the same direction; that is, during the uniform rotation of screw 23, when oscillation ends, screw 23 continues to rotate in the same direction. Rotating at a constant speed.

[0097] like Figure 10 The diagram shows the rotation of screw 23 when V2=0, after the sum of its uniform rotational angular velocity and its reciprocating angular velocity. Specifically, during the uniform rotation of screw 23, when oscillation occurs, the screw 23 experiences a cycle where its rotational speed increases to V1 and rotates for a period, then decreases to V2=0 and pauses for a period. This cycle repeats until the oscillation ends, at which point screw 23 continues its rotation. Rotating at a constant speed.

[0098] like Figure 11The diagram shows the rotation of screw 23 when V2 < 0, after the sum of its uniform rotational angular velocity and its reciprocating angular velocity. Specifically, during the uniform rotation of screw 23, when oscillation occurs, the screw 23 experiences a cycle where its rotational speed increases to V1 for a period, then decreases to V2 < 0, and rotates in the opposite direction for a period. This cycle repeats until the oscillation ends, at which point screw 23 continues its rotation. Rotating at a constant speed.

[0099] like Figure 12 The diagram shows the rotation of screw 23 when its initial oscillation angular velocity is opposite to its uniform rotation angular velocity, and the sum of the uniform rotation angular velocity and the oscillation angular velocity of screw 23, resulting in V2 > 0. Specifically, during the uniform rotation of screw 23, when oscillation occurs, the screw 23's rotational speed decreases to V2 > 0, rotates for a period, then increases to V1 and rotates for a period; this process repeats until the oscillation ends, at which point screw 23 continues to rotate at a constant speed. Rotating at a constant speed.

[0100] The single-screw extruder includes a programmable logic controller (PLC). The servo motor and reducer are respectively connected to the PLC via wired or wireless communication. The PLC controls the screw 23 to rotate at variable angular speed. By cooperating with the reducer, the PLC controls the servo motor, so that the servo motor drives the screw 23 to regularly increase and decrease speed. Due to inertia, the material undergoes regular compression in the axial direction, which strengthens the local compression effect and is beneficial for compressing and compacting solid powder and for pushing and conveying it.

[0101] During operation, the barrel 21 of the single screw extruder 2 is divided into two working sections: the first section is the single screw conveying section, and the second section is the plunger extrusion section; the lengths of the first section and the second section can be set according to process requirements.

[0102] In the first section, which is a single-screw conveying section, the material is kept in a solid state and conveyed by the rotation of the screw. Specifically, the material is kept in a solid state and will not adhere to the screw wall. In this section, it is only compressed and compacted. Its working mechanism follows the solid conveying theory.

[0103] In the second stage, the back pressure generated by the rotation of the screw in the equipment is used to move the material forward; its working mechanism is similar to the principle of plunger extrusion. Furthermore, in the second stage, the working temperature is much higher than the melting point of UHMWPE, and the material melts and homogenizes.

[0104] UHMWPE melt is extruded through a single-screw extruder 2, and then UHMWPE rods 7 are prepared through an extrusion die 3, a cooling and shaping section 4, a traction guide rail 5, a pneumatic cutter 6, and a cooling water machine. The extrusion die 3 can use different molds, allowing for the extrusion of strip materials with different cross-sectional shapes. In this embodiment, a circular die 3 is used, extruding cylindrical rods. This preparation device can continuously process UHMWPE powder with a viscosity-average molecular weight of 2 million to 6.5 million into cylindrical rods with a maximum diameter of 80 mm without adding any processing aids. Furthermore, the use of periodic variable angular velocity rotation superimposed with circumferential oscillation extrusion technology increases the production line speed of the rods by 25% and the impact toughness by 20%, making it suitable for producing ultra-clean medical-grade UHMWPE molding compounds (ash content ≤100%). UHMWPE powder (ppm) can be used to manufacture artificial joint prostheses, as well as high wear-resistant pads or impact-resistant wear-resistant parts for large machinery, such as bearings and gears. It should be noted that medical-grade UHMWPE powder can be used for manufacturing high wear-resistant pads or impact-resistant wear-resistant parts for large machinery, such as bearings and gears.

[0105] In this embodiment, the processing parameters set in step S2 are the control parameters for the variable angular velocity rotation of the screw 23; specifically, the uniform rotation speed, oscillation frequency, and oscillation amplitude of the screw 23. Preferably, the uniform rotation speed is 0.5–5 rpm, the oscillation frequency is 0.1–2 Hz, and the oscillation amplitude is 1.57–6.28 rad. Within these conditions, the extrusion efficiency of the bar can be maximized while ensuring that unstable extrusion phenomena such as melt fracture do not occur.

[0106] In this embodiment, in order to facilitate monitoring of the temperature and pressure of the extrusion die, a thermocouple and a pressure sensor are provided on the extrusion die, and the pressure of the extrusion die is adjusted by changing the rotation speed of the screw 23 and the temperature of the barrel 21.

[0107] In this embodiment, the temperature of the barrel 2 is divided into seven sections from the feed inlet to the extrusion die. The temperature of the first to the fourth section gradually increases, and the temperature of the fourth to the seventh section gradually decreases. The seven heating sections in the barrel 21 can be configured with appropriate dimensions according to specific process requirements.

[0108] In this embodiment, the temperature adjustment range of the barrel 21 is between 90°C and 260°C.

[0109] In this embodiment, preferably, the temperature of the barrel 21 is 90°C, 180°C, 220°C, 260°C, 250°C, 240°C, and 180°C respectively from the first segment to the seventh segment.

[0110] In this embodiment, preferably, the pressure of the extrusion die 3 is controlled to be less than or equal to 60 MPa in step S2.

[0111] In another embodiment, since excessive die pressure will cause the product to swell significantly after extrusion, resulting in a rough product surface and increased equipment load, the pressure of the extrusion die is less than 20 MPa.

[0112] In another embodiment, the pressure of the extrusion die 3 can be controlled to be less than 10 MPa. At this pressure, the quality of the product is best, and the load on the equipment is optimal.

[0113] In this embodiment, preferably, the screw 23 has a diameter Φ of 70 mm and an aspect ratio of 26:1. The diameter of the screw 23 depends on the cross-sectional size of the product; this diameter screw 23 is suitable for extruding rod products with a diameter of 80 mm. A larger aspect ratio results in better plasticizing effect, but an excessively large aspect ratio can also cause the screw 23 to bear excessive torque and lead to material degradation due to longer residence time. 26:1 is a more suitable aspect ratio for the screw 23 when processing UHMWPE rods.

[0114] Example 1:

[0115] A pure UHMWPE rod with a diameter of 80 mm is prepared using the preparation method and apparatus provided in this invention, comprising the following steps:

[0116] (1) Select UHMWPE powder: viscosity-average molecular weight 292×10 4 g / mol, bulk density 0.45 g / cm³ 3 Ash content 69 ppm.

[0117] (2) The selected UHMWPE powder is added into the barrel 2 through the feed port and processed into shape using a single screw extruder, extrusion die, cooling and shaping device, traction guide rail and pneumatic cutting machine. The screw 23 rotates in a variable angular velocity manner by superimposing circumferential uniform rotation and reciprocating oscillation. The uniform rotation speed (v) is 1.5 rpm (4.7 rad / s), the oscillation frequency (f) is 0.2 Hz and the oscillation amplitude (θ) is 3.14 rad.

[0118] (3) The temperature of the barrel 21 is divided into 7 sections from the feed port to the extrusion die. The temperatures of the 1st to the 7th sections are 90℃, 180℃, 220℃, 260℃, 250℃, 240℃ and 180℃ respectively. The extrusion die pressure is 6-8MPa. The cooling medium of the curing section is cold water.

[0119] Example 2:

[0120] A pure UHMWPE rod with a diameter of 80 mm is prepared using the preparation method and apparatus provided in this invention, comprising the following steps:

[0121] (1) Select UHMWPE powder: viscosity-average molecular weight 439×10 4 g / mol, bulk density 0.46 g / cm³ 3 Ash content 93 pp.

[0122] (2) The selected UHMWPE powder is added into the barrel 21 through the feed port and processed into shape using a single screw extruder, extrusion die, cooling and shaping device, traction guide rail and pneumatic cutting machine. The screw 23 rotates in a circumferential uniform rotation superimposed with a reciprocating oscillation variable angular velocity rotation. The uniform rotation speed (v) is 1.5 rpm (4.7 rad / s), the oscillation frequency (f) is 0.2 Hz and the oscillation amplitude (θ) is 3.14 rad.

[0123] (3) The temperature of the barrel 21 is divided into 7 sections from the feed port to the extrusion die, with the first section being 90℃, 180℃, 220℃, 260℃, 250℃, 240℃ and 180℃ respectively; the extrusion die pressure is 7~10MPa; the cooling medium of the curing section is cold water.

[0124] Example 3:

[0125] A pure UHMWPE rod with a diameter of 80 mm is prepared using the preparation method and apparatus provided in this invention, comprising the following steps:

[0126] (1) Select UHMWPE powder: viscosity-average molecular weight 657×10 4 g / mol, bulk density 0.36 g / cm3, ash content 32 ppm.

[0127] (2) The selected UHMWPE powder is added into the barrel 21 through the feed port and processed into shape using a single screw extruder, extrusion die, cooling and shaping device, traction guide rail and pneumatic cutting machine. The screw 23 rotates in a variable angular velocity manner with circumferential uniform rotation and reciprocating oscillation. The uniform rotation speed (v) is 1 rpm (3.14 rad / s), the oscillation frequency (f) is 0.1 Hz and the oscillation amplitude (θ) is 1.57 rad.

[0128] (3) The temperature of the barrel 21 is divided into 7 sections from the feed port to the extrusion die, with the first section being 90℃, 190℃, 240℃, 280℃, 260℃, 240℃ and 190℃ respectively; the extrusion die pressure is 14~18MPa; the cooling medium of the curing section is cold water.

[0129] Comparative Example 1:

[0130] A pure UHMWPE rod with a diameter of 80 mm was prepared, using the same UHMWPE powder as in Specific Example 1; the screw rotated at a constant speed (v) of 1.5 rpm (4.7 rad / s), and other processing parameters were the same as in Example 1.

[0131] Comparative Example 2:

[0132] A pure UHMWPE rod with a diameter of 80 mm was prepared, using the same UHMWPE powder as in Example 2; the screw rotated at a constant speed (v) of 1.5 rpm (4.7 rad / s), and other processing parameters were the same as in Example 2.

[0133] Comparative Example 3:

[0134] A pure UHMWPE rod with a diameter of 80 mm was prepared, using the same UHMWPE powder as in Example 3; the screw rotated at a constant speed (v) of 1 rpm (3.14 rad / s), and other processing parameters were the same as in Example 3.

[0135] The preparation method and apparatus used in this invention enable continuous and stable molding of pure UHMWPE rods. The maximum diameter of the prepared rods reaches 80 mm. The rods have a smooth surface and dense material. Cross-sectional observation shows that the internal structure is uniform and defect-free (see...). Figure 5 In terms of mechanical properties, for all molecular weights examined (2.9 million to 6.5 million), rods prepared by extrusion technology involving circumferential uniform rotation superimposed with reciprocating oscillation at variable angular velocity showed significantly improved tensile strength compared to conventional methods (uniform screw rotation), while maintaining a high level of elongation at break (see [link to extrusion process]). Figure 6 The specific tensile properties are listed in Table 1, which compares the performance of the UHMWPE rods prepared (specific examples) with those obtained by conventional methods (comparative examples).

[0136] Table 1

[0137] Example 1 292 69 25 168 26.8 55.5 559 Example 2 439 93 24 132 24.7 51.7 431 Example 3 657 32 20 92 24.6 44.6 391 Comparative Example 1 292 69 21 94.9 22.8 39.7 578 Comparative Example 2 439 93 19 82.3 20.2 38.3 564 Comparative Example 3 657 32 16 77.5 18.4 34.2 535

[0138] Table 1 shows that the continuous molding of UHMWPE rods using the preparation method and apparatus provided by this invention (variable angular velocity screw rotation) increases production efficiency by 19%–25% compared to conventional molding methods (uniform screw rotation); furthermore, it significantly improves the mechanical toughness of the rods. The lower the molecular weight, the more significant the improvement in toughness, with the impact strength increase reaching up to 75%. Therefore, the UHMWPE rods prepared using the preparation method and apparatus provided by this invention have higher production efficiency and significant performance advantages compared to existing molding methods. Since the UHMWPE raw material used meets medical implant-grade cleanliness standards, the pure UHMWPE rods provided by this invention are highly suitable for manufacturing artificial joint prostheses, generating extremely high added value.

[0139] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing ultra-high molecular weight polyethylene rods by continuous molding, characterized in that, Includes the following steps: S1. Select pure UHMWPE powder; S2. Add the selected UHMWPE powder to a single-screw extruder, set the processing parameters, and after high-temperature plasticizing, continuous extrusion, rod cooling, and finally cutting into shape; The screw (23) of the single screw extruder uses a variable angular velocity rotation mode of uniform rotation superimposed with circumferential reciprocating oscillation to extrude and extrude UHMWPE powder; Step S2 uses a continuous molding equipment for ultra-high molecular weight polyethylene rods to prepare UHMWPE rods. The equipment for the continuous molding of ultra-high molecular weight polyethylene rods includes a single screw extruder (2), a power control box (1), an extrusion die (3), a cooling and shaping device (4), a traction guide rail (5), and a pneumatic cutting machine (6). The single-screw extruder (2) has a barrel (21) and a screw (23); A threaded structure (22) is provided on the inner wall of the barrel (21), and the thread direction of the threaded structure (22) is opposite to the thread direction of the screw (23); The single screw extruder (2) is driven by a servo motor for its screw (23). The single screw extruder is equipped with a reducer, which is connected to the servo motor for transmission. The single screw extruder also includes a controller. The servo motor and reducer are respectively connected to the controller for communication. The controller is used to control the screw (23) to rotate at a constant speed and rotate at a variable angular velocity by superimposing circumferential reciprocating oscillation. The barrel (21) of the single screw extruder (2) is divided into two working sections: the first section is the single screw conveying section and the second section is the plunger extrusion section; the lengths of the first section and the second section are set according to the process requirements. In the first single-screw conveying section, the material remains in a solid state and is conveyed by the rotation of the screw; its working mechanism follows the theory of solid conveying. In the second plunger extrusion section, the back pressure generated by the rotation of the screw of the equipment is used to move the material forward; its working mechanism is similar to the principle of plunger extrusion, and the working temperature in the second section is higher than the melting point of UHMWPE, so that the material melts and homogenizes.

2. The method for preparing ultra-high molecular weight polyethylene rods by continuous molding according to claim 1, characterized in that, The molecular weight of the UHMWPE powder in step S1 is 2 million to 6.5 million.

3. The method for preparing ultra-high molecular weight polyethylene rods by continuous molding according to claim 2, characterized in that, The processing parameters set in step S2 include the control parameters for the screw (23) rotating at a constant speed and then rotating at a variable angular velocity in a circumferential reciprocating oscillation; specifically, the constant speed rotation angular velocity, oscillation frequency and oscillation amplitude of the screw (23); The screw (23) rotates at a constant angular velocity of The angular velocity of the reciprocating oscillation of the screw (23) is ; ； In the formula, f is the oscillation frequency. This refers to the amplitude of the oscillation. The angular velocity of the screw (23) rotating at a constant speed and the angular velocity of the screw (23) reciprocating oscillation are superimposed to obtain the positive superimposed velocity V1 and the negative superimposed velocity V2; ； ； Where, when V2 > 0, the direction of rotation of V2 is... The rotation direction is the same as that of V2; when V2 < 0, the rotation direction of V2 is the same as that of V2. The rotation direction is opposite.

4. The method for preparing ultra-high molecular weight polyethylene rods by continuous molding according to claim 1 or 3, characterized in that, The extrusion die (3) is equipped with a thermocouple and a pressure sensor.

5. The method for preparing ultra-high molecular weight polyethylene rods by continuous molding according to claim 4, characterized in that, In step S2, the temperature of the barrel (21) is divided into 7 segments from the feed inlet to the extrusion die. The temperature of the first segment to the fourth segment gradually increases, and the temperature of the fourth segment to the seventh segment gradually decreases. The temperatures of the barrel (21) in the first to seventh sections are 90℃, 180℃, 220℃, 260℃, 250℃, 240℃ and 180℃ respectively.

6. The method for preparing a continuous molding of ultra-high molecular weight polyethylene rods according to claim 4, characterized in that: In step S2, the pressure of the extrusion die (3) is controlled to be less than or equal to 60 MPa; the screw (23) of the single screw extruder (2) has a diameter of 70 mm and a length-to-diameter ratio of 26:

1.

7. A method for preparing ultra-high molecular weight polyethylene rods by continuous molding according to any one of claims 1 to 6, characterized in that: The prepared ultra-high molecular weight polyethylene rods are used in medical artificial joint prostheses, high wear-resistant pads, or impact-resistant and wear-resistant parts of large machinery.

8. A method for improving the mechanical properties of ultra-high molecular weight polyethylene rods, characterized in that, The method includes the following steps: S1. Select pure UHMWPE powder; S2. Add the selected UHMWPE powder to a single-screw extruder, set the processing parameters, and after high-temperature plasticizing, continuous extrusion, rod cooling, and finally cutting into shape; The screw of the single-screw extruder uses a working mode of uniform rotation superimposed with circumferential reciprocating oscillation to extrude and extrude UHMWPE powder; Step S2 uses a continuous molding equipment for ultra-high molecular weight polyethylene rods to prepare UHMWPE rods. The equipment for the continuous molding of ultra-high molecular weight polyethylene rods includes a single screw extruder (2), a power control box (1), an extrusion die (3), a cooling and shaping device (4), a traction guide rail (5), and a pneumatic cutting machine (6). The single-screw extruder (2) has a barrel (21) and a screw (23); A threaded structure (22) is provided on the inner wall of the barrel (21), and the thread direction of the threaded structure (22) is opposite to the thread direction of the screw (23); The single screw extruder (2) is driven by a servo motor for its screw (23). The single screw extruder is equipped with a reducer, which is connected to the servo motor for transmission. The single screw extruder also includes a controller. The servo motor and reducer are respectively connected to the controller for communication. The controller is used to control the screw (23) to rotate at a constant speed and rotate at a variable angular velocity by superimposing circumferential reciprocating oscillation. The barrel (21) of the single screw extruder (2) is divided into two working sections: the first section is the single screw conveying section and the second section is the plunger extrusion section; the lengths of the first section and the second section are set according to the process requirements. In the first single-screw conveying section, the material remains in a solid state and is conveyed by the rotation of the screw; its working mechanism follows the theory of solid conveying. In the second plunger extrusion section, the back pressure generated by the rotation of the screw of the equipment is used to move the material forward; its working mechanism is similar to the principle of plunger extrusion, and the working temperature in the second section is higher than the melting point of UHMWPE, so that the material melts and homogenizes.

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